Forum OpenACS Q&A: here is a faster util_memoize for 3.2.x

for those of you with 3.2.x sites, here is a drop-in replacement for util_memoize that is about 30% faster thanks to using catch {nsv_get ...} rather than a separate nsv_exists calls.

proc_doc util_memoize {tcl_statement {oldest_acceptable_value_in_seconds ""}} {
    Returns the result of evaluating the Tcl statement argument
    and remembers that value in a cache; the memory persists
    for the specified number of seconds
    (or until the server is restarted if the second argument is not supplied)
    or until someone calls util_memoize_flush with the same Tcl statement.
    Note that this procedure should be used with care because it calls the
    eval built-in procedure (and therefore an unscrupulous user could do Bad Things.
} {
    # we look up the statement in the cache to see if it has already
    # been eval'd.  The statement itself is the key
    if {[catch {
            set statement_value [nsv_get util_memoize_cache_value $tcl_statement]
        }] \
        || (![empty_string_p $oldest_acceptable_value_in_seconds] \
            && [nsv_get util_memoize_cache_timestamp $tcl_statement] + $oldest_acceptable_value_in_seconds < [ns_time]) \
    } {
        # not in the cache already OR the caller spec'd an expiration
        # time and our cached value is too old

        set statement_value [eval $tcl_statement]
        nsv_set util_memoize_cache_value $tcl_statement $statement_value
        # store the time in seconds since 1970
        nsv_set util_memoize_cache_timestamp $tcl_statement [ns_time]
    }

    return $statement_value
}